Abstract

This study was designed to further characterize peripheral skeletal muscle alterations in patients with chronic obstructive pulmonary disease (COPD) and to evaluate the possible relationship between myosin heavy chain (MyoHC) isoform expression and exercise tolerance in these individuals. MyoHC composition from biopsy of the vastus lateralis muscle was examined in 12 COPD patients (forced expiratory volume in one second (FEV1)=31+/-9% predicted, peak oxygen consumption (V'O2)=15+/-4 mL x kg(-1) x min(-1)) and 10 age-matched normal male subjects (peak V'O2=20+/-5 mL x kg(-1) x min(-1)). The proportion of MyoHC type I was smaller in COPD than in normals (27+/-17% versus 41+/-9%, p<0.05) with an increase in MyoHC type IIa (51+/-15% versus 39+/-9%, p<0.05) and the proportion of MyoHC type IIx being comparable between both groups. A significant relationship was found between peak V'Oo2 mL x kg(-1) x min(-1) and FEV1 % pred (r=0.91, p<0.0001) and the percentage of MyoHC type I (r=0.61, p=0.016). In stepwise multiple regression, only FEV1 % pred was found to be a significant determinant of peak V'O2 (p<0.0001). This variable explained 83% of the total variance of peak V'O2. In summary, this study showed considerable modifications in the phenotypic expression of the myosin heavy chain in the vastus lateralis muscle in patients with chronic obstructive pulmonary disease. An independent effect of myosin heavy chain expression on exercise capacity was not found. These results suggest that chronic inactivity and muscle deconditioning may not be the sole factors explaining peripheral muscle dysfunction in patients with chronic obstructive pulmonary disease.